Methane (CH.sub.4) is known as a useful source of energy for heating purpose and as fuel for internal combustion engines for the driving of working machines or for the production of electric power. By means of anaerobic microorganisms methane can be produced with a biological mass as substrate. As biological material can for example manure from cowsheds or swineries, vegetable or animal waste from farms and food-production industries be used. Also sewer sludge can be utilized, if it substantially contains organic material. In order to carry out the process, there are certain requisites, which are important to fulfil in order to obtain a high yield of gas, a reasonable processing time, a high plant utilization factor, and low handling costs, viz.:
(1) The process should be continuous, so that the culture of the microorganisms can be maintained for an uninterrupted gas production; PA1 (2) Biological material should be continuously supplied and removed, so that the capacity of the plant due to volumetric efficiency can be utilized to the greatest possible extent, and any periods of standstill for supply and removal of material will not be required; PA1 (3) The process should take place at such a temperature that a reasonable processing time and a high gas yield will be obtained; PA1 (4) The handling of material should be automatic, preferably by means of pumps and not involve any essential manual labour.
Especially in large plants of capacity in the order of a few or several hundred cubic meters of substrate, these requisites have turned out to be difficult to fulfil by the technique of the prior art. Thus, a heating is necessary by use of types of anaerobic microorganisms, which in plants of the said size means a considerable sacrifice of costs with respect to construction and energy.